1. Field of the Invention
The present invention relates to flexible couplings for rotatable shafts, and more particularly, to couplings permitting both angular and axial misalignment between coupled shafts.
2. Description of Prior Art
In order to accommodate misalignment and torque, flexible couplings have been employed between rotatable shafts having fixed or variable misalignment. Such couplings are connected typically about peripheral flanges so as to transmit torque from one shaft to the other shaft while absorbing and sometimes dissipating the effects of misalignment. An example of one type of such flexible couplings is described in U.S. Pat. No. 2,647,380.
The practical coupling construction of the prior art is shown in FIG. 5 where coupling member 110 comprises body 112 and two peripheral flanges 114. Body 112 has two axially separated disk portions 116, which extend radially outward from the axis of rotation, and annular hub portion 118. The massive hub portion 118 is rigid and heavy, accounting for a large percentage of the weight of the entire coupling member 110. Peripheral flanges 114 are formed at the outer ends of disk portions 116 of body 112 such that both peripheral flanges 114 rotate about the axis of rotation.
Such conventional couplings have a major disadvantage: limited degree of flexibility. For a given misalignment, the coupling member is subjected to high stresses. The coupling member responds with high reaction forces transmitted to the connected equipment. If during operation the misalignment changes due to unforeseen circumstances, the flexible element may fail due to fatigue fractures. In addition, if the connected machines are modified to result in an increase in misalignment compared to the original set-up, the coupling member must be redesigned or configured to avoid costly failures. One common way of increasing misalignment tolerance is to incorporate additional flexible elements 110, thereby resulting in a heavier and more expensive construction.
Limited flexibility results primarily from the massive hub portion 118. As shown in FIG. 5, hub portion 118 occupies approximately 15% to 30% of the available Rt-Ri envelope (i.e., the space wherein body 112 is located). Since hub portion 118 is rigid, flexibility is limited to the disk portions 116 in the remaining 70% to 85% of the Rt-Ri envelope.
Fatigue fractures primarily result from structural designs that are too rigid to tolerate either steady or transient deformations of the coupling in use. For example, the structural design shown in FIG. 5 generally experiences fatigue fractures in the thin disk portion 116.
Accordingly, a structural design is desired which significantly reduces fatigue and stress fractures from increased misalignment, and which is more flexible and lighter without adding to the fabrication cost.